Dehydration of aqueous isopropanol



July 22, 1952 J. D. BROOKS ET AL 2,604,440

DEHYDRATION OFAQUEOUS ISOPROPANOL Filednec. 1, 1949 n Henri; O, motten?.

" @4A/ Cltboraeg Patented July 22, v1952 Bloomfield, N. J., assignors to Standard Oil Development Company, a`. corporation of Delaware Y l This invention relates tothe of'fwater lfrom aqueous isopropanol. More particularly the invention relates to a process for drying isopropanol which comprises fractionally distilling aqueous isopropanol in the presence of 30 to 65 Wt.

hindered by the fact thatfthe binary azeotrope 4distills yover from the fractionating column.

- *It is anl object therefore of this invention to provide, a process for the removal: of water from aqueous isopropanol.

It is also an object of this invention to provide a distillation process forl breaking the isopropanol-Water binary azeotrope whereby a vapor richer in isopropanolthan the azeotrope will distill overv from the distillation zone.

The invention will be more readily.. understood v by reference to the accompanying drawing which is yadiagrammatic vflow plan of apparatus employed in one preferable embodimentv of the invention. l' v.

llleferringl to thedrawing numeral 2 represents a distillationcolumn of the usual' type equipped -with suitable' trays, bubble caps, etc.' To vthe ,column there is fed via line I an aqueous iso- UVpropanol, for example aqueous isopropanol of the binary azeotrope composition, i.' e., 91.3 vol.

isopropanol-8.7 vol. Water. Thevfeed is introduced into column 2 at apoint at or near its midpoint. sulfuric acid v,is introduced into the top of the distillationmcolumn via line 3 at a point above the alcohol feed point. Heat is applied to the base of the column by suitable means such as by steam coil 4. Y'During the distillation process the alcohol vapors pass up the column and are contacted countercurrently by the sulfuric acid which descends the column from its point. of addition above. The acid extracts water from the alcohol vapors and thereby becomes diluted.` It is essential howevertomaintain' the concentration of the acid in`z gcontact with the alcohol in the columnv at a strengthof 30'to 65 Wt. preferably about 40 to '45 wt'. If the acid falls below approximately 30 wt. no dehydration of the isopropanol takes place, while if the acid strength exceeds approximately 65 wt. chemical reaction of the alcohol to isopropyl ether and propylene and other materials occurs. Vapors of isopropanol richer in the al- 4 g 6 clanes. (c1. 2021-68) 2 Y cohol than the binary azeotrope are removed from column 2 via linei5`, condensed in condenser 6 and removed from the system via pipe 1.

There is withdrawn as bottoms from column 2 via line B a mixture of diluted aqueous sulfuric acid containing some small dissolved quantities of-isopropanol, Vusually less than'1%." In breaking the isopropanol-water,binary azeotropevit is preferred tov add sulfuric acid of to 65 wt. concentration to the tower in amounts sufficient to maintain an aqueousv acid'bottomsin the tower of about '40-45 wt. acid concentration. This latter mixture is led to distillation column 9 equipped with heating means I0 such as a closed steam coil. In tower Ily the mixture is distilled to strip therefrom isopropyl alcohol which is taken overhead via line II. l The overhead will contain less alcohol thanV is present in the aqueous azeotrope. that is, its content will be less than 91 vol.-% isopropanol. The bottoms from this column is removed via line I4 and sent to reboiler I5 whereinthelsulfuric acid is concentrated to the original strength of 30 to 65 wt. Steam resulting' from the reconcentrationl-is passed via line I6 into Va rpoint near the bottom of tower 9 in order to assist inthe distillation of the acid-alcohol mixture. The reconcentrated acid is returned via line I1 to acid feedv line 3. Fresh acid is added, if desired, via line I8. The aqueous alcohol' recovered overhead via line II is fed toga third distillation column I2, heated by appropriatel means, such' as steam coil I9. Additional crude aqueous isopropanol, such as isopropanol of 60-70 vol. concentration, may be added with this feed via line 'I3 or directly to column I2. In column I2 the isopropanol'isV concentrated to thebinary azeotrope which is re-v moved overhead via line 20 and returned to feed line I. Excess water is removed from the' system vialine2I. j Vjv The nature'and the concentration of the iacid employed Vin this process isV important. Ithas been found that benzenesulfonicacid cannotjbe ysubstituted forl the' sulfuric'acid. j On the contrary isopropanol dehydrates the benzene sulfonic acid. Acid salts which act like acids in aqueous solution likewise do not function successfully. For example, aqueous solutions of s odiumhydrogen sulfate when employed in the distillation process fail to produce an overhead alcohol containing more alcohol than the binary' azeotrope. Sodium hydrogen phosphate in aqueous solution produced in the distillation process an alcohol overhead scarcely above the binary azeotrope composition.

' sulfuric acid and ofO Wt. 7c sulfuric'acid. T liere Aqiicciisphcspiicric acid, however, is suitable as a substitute for sulfuric acid. For example, a 45 wt. solution of phosphoric acid when ernployed inthe process produces an alcohol Vapor containing more alcohol than the binary azeotrope. However, this acid is vnot as effective for the removaljjcf Water as is sulfuric acid.V l

The process cannot be applied analogously'to other alcohols. were made to remove Water from aqueous eth- For example, when attemptsl l() anol employing either 45 yvt;i% sulfuric acid or 50% benzene sulfonic acid, itwas. discoveredvin each case that ethanol proved t behthe'bettcr dehydrating agent. Witlrfsccn y butanol, sulfuric acid of 35-65-Wt. concentrationproduced rapid decomposition of the alcohol to ole- Example AkV1 i' employing an acid of 35 wt. concentration. fVaporsvpontaining93.13 vol. isopropanol Were obtained. These vapors are 1.83 vol. richer in alcohol than the binary azeotrope.

n. Lower concentrations of sulfuric-acid wercf found to be ineffective for the removal of water.

The invention is illustrated Vby the l-follh'irg' Y"werfe removedfrom theV distillation column.

xamplel! nThey above e'pe'ri'mnt was repeated withjfonly sufficient 651m. Hcsoi added` tpriircducc :a

'fm1 acid cciicciiirati'c'n cf so wt, in ihcicwcr section'y of Ythe' column below 'the alcohol -feed plate. An alcohol vaporc'ontaining 92.93 y'ol.

isopropanolfwas obtained from'the distillation Eampzcfirr' The experiment of rliiainple"I Wasfrepead adding only sufficient acid toproduce a final acid r4.5

concentration of 2-5 wtf inV thelower section k-of the column. vAn"alcolilolvapor was ob'ts'iincd containing 9 1 .3fvc1. t fiscpicpanci whichictiic alcohol content of the aqueous rbinary `aseotrope. This experiment indicates thatzfyvt.

the isopropanol-Water binary azeo'tro'pei 'fEalmpZe "IV Y stillin the presence of l0 v0l.f% ofjfi,A

was 'no evidence of olefin or etherf 'canbe'tolerated in theiisopropanol product. j Emamfzc V 'the' vlicciiipcsiiiic'ri"clicka of `sulfuric acid onisopropanol, '9 9 vol. is o propanol Wasboiledina vapor liquid 'equilibrium Y Number,

. Example VII The distillationof Example V was repeated employing 45 wt. 7c H3PO4. Vapors containing 93.8 vol.y isopropano1 were obtained. This distillate 'is '2.5 v01. richer in isopropanol than the binary azeotrope.

.What is claimed is: f l

l. A process for dehydrating an isopropanolwater binary a'zeotrope which comprises distilling the azeotrope ina distillation 'zone in the Vpresence of 30'65 wt. sulfuric acid, and removing from the distillation Zone a distillate containing a greater .proportion"of'isopropanol than is present in `said va'zeotrope.v f

2. A process according to claim 1V in which sulfuric acid is approximately 40-45 wt.

3. Aprocess' for `dehydrating an Visopropanolnic Water binary azeotrope' which comprises passing theazeotrope in the vapor phase in a distillation Zone coun'tercurrently to 'and kin 'contactfwi'th aqueoussulfuric acid iof3065 Wt."% acid concentration, ,and removing from `the distillation zone a distillate containing` "a lgreater proportion of isopropanolthanV the biaryazeotrope 4. A process according to claim 3 in which the sulfuric acid is 40"-45 wt. Iconcentration'.v f

l5. Av process for producing f-isopropanol' containing less Water :than the Visopropanol.-vvater binary Yazeotr'ope from aqueous isopropanol'containingdnore Waterithan .t'l'ie binary azebtrope Whichicomprises, -distilling thelatter 'aqueusiso- Ipropan-ol ina distillation zone Vtoremovethere'- from a distillate comprising the isopropanol-.Wahter binary azeotrope, passingthe azeotrope'iinthe vapor phase in a secondfdistillation 'zonecoun- Vtercurrently to and in contact With aqueousuln.furie acid of ,130s-65 Wt. -acid concentration, and :removing from the'iseco'nd'idistillation` Zone a distillate of isopropanol containing- :less water .than the binary VVazeotrope. I

. 6 A process according to, claim' in 'Which-the -sulfuric acidis of 40- 45 concentration;

The following references yare of lrecordi'n 'the le of this patent: Y v f UNITED 'iSA'f/rsf f The distillation of Example V was repeated' 

1. A PROCESS FOR DEHYDRATING AN ISOPROPANOLWATER BINARY AZEOTROPE WHICH COMPPRISES DISTILLING THE AZEOTROPE IN A DIISTILLATION ZONE IN THE PRESENCE OF 30-65 WT. % SULFURIC ACID, AND REMOVING FROM THE DISTILLATION ZONE A DISTILLATE CONTAIN- 